Is there a bye-law that says that I need a bell on a towpath?

In my opinion if you're going faster than running pace on a shared path you're going too fast. As Oliver said they're a place for a poodle.

Where did Oliver say that?

Anyway, even if I wasn't on a bike I wouldn't want someone else's do sniffing/barking at me so why accept it on a bike. What's wrong with putting stupid dog on leads.
I'm not against dogs in general, I absolutely adore my mates dogs but that's because they do as they're told then and there.